We were told (more than ten times) NOT to memorise any knowledge, but to understand everything in systems.
A system has regulatory forces, and these forces are known as positive or negative feedback.
A negative feedback is something that discourages the change. For example, when you exercise, your body heats up (the change), but you sweat, which cools your body down (the negative feedback). And negative feedback can be good, even if it's negative.
A positive feedback is a reaction that encourages the change. For example, water vapour is a greenhouse gas, so it will trap heat from the sun and cause the Earth to heat up. Because of this, more water will evaporate, and then more water vapour will built up in the atmosphere, causing the Earth to heat up further, which causes more water to evaporate and so on and so on and so on.
Then, we talked about the Carbon Cycle. This is a drawing of it. (The words are microscopic, so you may have to squint and guess.)

The black arrow labelled burning (if you really can't ready microscopic print), was caused by (guess who?) us human beings. That is why there is an increase in the amount of carbon dioxide in the air, which has led to the enhanced greenhouse effect. (This is a hint for our Climate Change essay, if you are talking about reducing carbon emissions)

The real reflection:
I thought the Carbon cycle was really interesting, because it was an example of how Mother Earth is completely made up of systems. Besides the Carbon Cycle, there is the Nitrogen Cycle, and the Water cycle, etc. Everything is somehow positioned perfectly so complement each other. For example, we do not need to worry about a shortage of water when we see the sea water evaporating, because it falls back down as rain again, and no water is actually lost. How the Earth is so flawlessly programmed amazes me.
(During this lesson, we also learned about how we needed to do an essay on Climate change.)

Goh Yi Sin JH404